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Mobile social networks (MSNs) enable users to discover and share contents with each other, especially at ephemeral events such as exhibitions and conferences where users could be strangers. Nevertheless, the incentive of users to actively share their contents in MSNs may be lacking if the corresponding cost is high. Besides, as users in MSN share contents in an impromptu way as they move, it makes them vulnerable to malicious users who may want to disseminate false contents. This is because users may not have knowledge about the peers they are socially connecting with in the network. In this paper, we propose MCoST, a mechanism that motivates content sharing in MSN and ensures that only trustworthy contents are shared. The mechanism is built on users� collective bidding, content cost sharing and trust evaluation while guaranteeing individual rationality. MCoST enables content providers to share contents with multiple users simultaneously by utilizing the broadcast nature of wireless transmission. The cost of the content is collectively compensated by the content receivers through the content bidding mechanism in MCoST. In ensuring that users can establish the trustworthiness of their encounters� contents, MCoST incorporates a robust trust evaluation framework that guarantees that content reviews are immutable and tamper-proof, resistive to sybil and rejection attacks, and that users cannot have multiple and fake identities in the network or reject negative reviews about their contents.
We consider an MSN at an exhibition with N users, so called attendees, who collect and share contents with their homophylic co-located encounters. Among these users, we define users who have collected some contents that they would consider sharing with their encounters as agents while users who wish to download contents hosted by agents as principals. During an encounter, agents share the metadata of the contents they wish to share. A content�s metadata con- tains its description and signed reviews from users who have experienced it. These reviews are hash-chained to form a review-chain to ensure that they are non-modifiable and non- deletable.
We first describe the content sharing framework. Normally, at a themed exhibition, attendees are interested in collecting contents that are trustworthy. As MSN has no central author- ity that can provide reference in regard to trustworthiness of agents and their contents, any principal interested in an agent�s content has to evaluate the trustworthiness of the con- tent by himself. The principal may then share his evaluation as a content review on the content�s metadata to assist the agent�s future principals to evaluate trustworthiness of his content.
Typically, users may encounter their homophylic peers at stands that are exhibiting on topics of common interest. Thus, we leverage these users� co-located peers at the stands for content sharing. Specifically, we consider that a user with content to share broadcasts the content�s metadata to her 1-hop neighbors during their co-location at a stand. Users interested in the content respond to the agent within the broadcast�s validity period specified in the metadata.
smart mobile devices and phones become more ubiq- uitous and pervasive with wide array of sensors and communication techniques, we can develop mobile social network (MSN) apps that enable these devices to automat- ically create virtual communities where contents can be shared implicitly. For instance, your smartphone could assist you have a productive encounter with other MSN users by informing you about their interests and valuable contents that they may share with you.
Example of such application is Whozthat which uses MSN to enrich offline social interaction among strangers by suggesting topics of common interest. An exhaustive discussion on structure and design of MSN, and its applications can be found in
we examine the design of MSN to enrich attendees� experience at a large scale exhibition. Exhibition attendees always want to gain insights of new developments in domains of their interests, and to interact with the exhibitors and fellow attendees. Most attendees would wish to visit all the stands and to participate in most activities which fall within their interests. However, as exhibitions run for a short duration (typically 3 ? 5 days) with many exhibitors, these attendees may not be able to visit all the relevant stands whose contents they may be interested in. Besides, it may be costly to individually visit all the stands to assess if their contents are of interest.
Nevertheless, we observe that the attendees may wish to discover and connect with their encounters whom they share with similar interests. Also, they may wish to record these offline contacts and transfer them to online social networks such as Facebook for future connections and interactions. This motivates us to utilize the short but frequent encounters at the exhibition to create an MSN as a platform for users to share and exchange their contacts and contents. Such an approach potentially boosts the speed and significantly reduces the cost of content collection.
We propose a novel mechanism that motivates content shar- ing and trustworthiness in mobile social network events such as an exhibition. The mechanism is built on collective bidding and cost sharing, and distributed cryptographic hash- chained content reviews that makes it resilient to sybil and rejection attacks.
Users propose payments for contents based on the contents trustworthiness while content owners share their contents only if the proposed payment can compensate the costs of sharing their contents with users who are inter- ested in them. This guarantees user�s individual rationality and thus promotes content sharing in the network and also ensures that the shared contents are trustworthy